The present invention relates to a hydraulic distributor designed to actuate a hydraulic actuator, for example a cylinder, by controlling the supply and outlet of the hydraulic fluid acting on the active surfaces of the movable member of the actuator itself. In particular, the distributor of the invention is designed to control automatically the rate of movement of said movable member so as to prevent its rate of movement from attaining excessively high values in any operating condition of the actuator.
Known hydraulic distributors intended to actuate an actuator normally comprise a slide valve designed to be brought from the rest position into two different positions, in each of which it connects hydraulically the source of fluid under pressure with a chamber of the actuator so as to actuate the movable member and, simultaneously, communicates the other chamber of said actuator with the outlet.
With distributors of this type, under certain operating conditions when the external force applied to the movable member of the actuator corresponds to the motive force generated by the pressure of the fluid on the movable member, the displacement of the movable member may occur at an excessively high velocity which is totally independent of the flow rate of the motive fluid fed into the actuator. In order to eliminate this disadvantage the hydraulic circuit, of which the distributor and actuator form part, is usually provided with valves throttling the flow of fluid towards the outlet so as to exert on the movable member of the actuator a back pressure capable of limiting the speed of forward movement thereof. With such a structural solution there is no strict control of the velocity of the movable member, since this velocity is not always proportional to the flow rate of fluid supplied to the actuator; furthermore, this control can take place only when the velocity of the movable member is within a well-defined range.